This invention relates to hot melt ink and, more particularly, to a new and improved hot melt ink which is effective to inhibit corrosion of the components of the system in which the ink is used.
Conventional printing systems for applying hot melt ink such as ink jet printers contain many components which are subject to corrosion resulting from contact with the ink. For example, piezoelectric transducers containing lead zirconium titanate, tin-lead alloy solder, nickel, aluminum, epoxy polymers, copper beryllium alloys and stainless steel are sensitive to either metallic or ionic impurities in the ink which can lead to rapid corrosion or electrochemical attack. Since typical chemical reaction rates increase by a factor of about 2 for every 10.degree. C. temperature rise, corrosion problems in hot melt ink jet systems which may operate at temperatures as high as 160.degree. C. are much more severe than those encountered in printing systems which operate at room temperature. On the other hand, many hot melt ink components, including stearic acid, paraffin wax, polyethylene wax, carnauba wax, candelilla wax, montan wax, hydrogenated castor oil, microcrystalline wax, behenic acid, aluminum stearate, synthetic ester waxes, oxidized polyethylene waxes, lauric acid, Fischer-Tropsch waxes, esparto waxes, dammar wax, oxazoline wax, bisamide waxes, amide waxes, oleamides, stearamides, lauramides, erucamide, glycerol monostearate, glycerol tristearate, chlorinated waxes, cetyl alcohol, stearone, laurone, diphenyl phthalate, dicyclohexyl phthalate, camphor, triphenyl phosphate, n-ethyl toluene sulphonamide, n-cyclohexyl-p toluene sulphonamide and others, as well as certain polymeric materials, such as cumarone-indene polymer, rosin, rosin ester, hydrogenated resins, cyclic ketone polymers, styrene allyl alcohol polymers, polystyrenes, polyvinyl toluene/methylstyrene polymer, alkyl hydrocarbon polymer, aryl hydrocarbon polymers, alkyl aryl hydrocarbon polymer, terpene polymers, styrene-acrylates, ethylene-vinyl acetates, polypropylene, gilsonite and other asphaltic materials, cyclic hydrocarbon polymer, halogenated polymers and polyester polymers can all cause measurable rates of corrosion of sensitive materials, such as components made of copper-beryllium, stainless steel and the like, at temperatures in the range from 120.degree. C. to 160.degree. C. Further, as described in Chemical Technology and Analysis of Fats & Waxes by Lewkowitsch and Warburton (Vol. 1, page 143), many molten higher fatty acids will react slowly with metals, such as copper, lead and the like, with the evolution of hydrogen, and it has been found that many waxes or waxlike materials corrode metals at elevated test temperatures even when the waxes are stated to be acid-free. In addition, there is the possibility that acidic degradation products may be generated during the hot storage of such molten waxes and polymers which could affect the physical properties of the ink.
Another component of a hot melt ink is the colorant which may be either a dye or a pigment. Exemplary colorants include the following list: solvent yellow 162, 79, 81, solvent orange 56, solvent brown 58, solvent red 122, 119, 100, solvent blue 70, solvent red 35, solvent black 27, 45, 47, solvent red 49, basic red 51, solvent violet 8, solvent blue 4, disperse yellow 64, solvent red 135, solvent red 195, disperse violet 26, solvent yellow 16, 56, 6, 7, 14, solvent red 1, 23, 24, 27, 49, solvent blue 35, solvent black 3, disperse orange 201, solvent yellow 93, disperse yellow 54, disperse red 60, solvent red 52, disperse violet 31, and the like.
Amongst pigments that may be successfully used are the following: pigment yellows 1, 3, 12, 13, 14, 16, 17, 73, 74, 81, 83, 97, 98, 106, 113, 114; pigment reds 2, 3, 4, 5, 6, 7, 8, 9, 12, 14, 37, 38, 48:1, 48:2, 48:3, 48:4, 57:1, 57:2, 57:3, 88, 122, 146, 147; pigment blues 15:1, 15:2, 15:3, 15:4, 56, 61, 61:1; and pigment blacks 1, 20, carbon black, acetylene black, bone black, lamp black, graphite, and the like.
These materials may contain trace amounts of acidic or corrosive compounds or, under conditions of prolonged hot storage, they may produce, or react or degrade to produce, corrosive compounds.
Although known anticorrosion agents have been added to materials such as ink to prevent or inhibit corrosion of components with which the ink comes in contact, many of those agents have been found to have little or no effect in inhibiting corrosion of printing system components by hot melt inks used at high temperatures. In addition, the use of those agents may modify the physical or optical properties of such inks in an undesirable way. For example, many anticorrosion or antioxidation agents containing, for example, butyrated hydroxytoluene, substituted benzimadazole, calcium oxide, calcium stearate, lead naphthenate, neutralized calcium sulphonate, neutral barium sulphonate, lead sulphonate, zinc sulphonate and organic bases, when added in the range of 1% to 3% to hot melt inks, were found to be substantially ineffective to inhibit corrosion or caused undesirable changes in the physical or optical properties of the ink.